JP3305155B2 - Groove machining method and method of manufacturing dynamic pressure bearing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a groove machining method for machining a dynamic pressure generating groove of a dynamic pressure bearing for generating a dynamic pressure in a fluid in a bearing gap by a screw pump action, and a method of manufacturing the dynamic pressure bearing. Things.

[0002]

2. Description of the Related Art A dynamic pressure bearing which generates a dynamic pressure in a fluid in a bearing gap by a screw pump action is provided on at least one of a bearing shaft and a bearing sleeve which are rotatably fitted to each other, in a spiral shape such as a herringbone groove. Dynamic pressure generating groove is required. Conventionally, as a method of processing such a dynamic pressure generating groove into a bearing shaft or a bearing sleeve, groove processing by etching has been generally used. However, in the etching process, the processing accuracy is greatly affected by the concentration of the etchant, performance degradation, and the like, and the number of steps is generally large and the time required for the processing is long, so that the productivity is low.

[0003] For this reason, in recent years, particularly when manufacturing a small-diameter dynamic pressure bearing, a method of forming a dynamic pressure generating groove by pressing a ball against the surface of a bearing shaft or a bearing sleeve and performing plastic working is widely used. Have been. This is to hold the ball harder than the workpiece such as the bearing shaft and the bearing sleeve in the ball holding hole on the outer peripheral surface of the tool shaft,
The ball is pressed against the workpiece, the surface layer is plastically processed, and the tool axis is rotated while transferring the ball shape. At the same time, the feed is performed in the axial direction. By doing so, spiral grooves of various shapes can be formed. Generally, the material of a workpiece such as a bearing shaft or a bearing sleeve is brass (Vickers hardness 150).
), And relatively inexpensive ball bearing hard balls (Vickers hardness of 700 to
900).

[0004]

However, according to the above-mentioned prior art, as described above, a ball for hardening a ball bearing or the like is used as a ball for groove machining, while a ball of a tool shaft for holding the ball is used. The area around the holding hole is often hardened to a hardness higher than the hardness of the ball bearing ball when machining the ball holding hole by electric discharge machining or the like. Tends to be scratched or the sphericity of the ball is significantly impaired. When the shape of the ball deteriorates in this way, the processing accuracy of the groove processing of the workpiece decreases, and when the surface of the ball is damaged, the scratch is directly transferred to the surface of the workpiece,
Inconveniences such as unnecessary cutting of the surface of the workpiece occur. As a result, in the process of machining the dynamic pressure generating grooves and the like on the bearing shaft and the bearing sleeve of the dynamic pressure bearing, the shape accuracy of the dynamic pressure generating grooves and the like becomes insufficient, so that a high-performance dynamic pressure bearing can be obtained. There is an unsolved problem that cannot be solved.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and has been developed in consideration of the following problems. An object of the present invention is to provide a groove processing method and a manufacturing method of a dynamic pressure bearing, in which the accuracy of groove processing of a dynamic pressure generating groove or the like of a bearing is not reduced.

[0006]

In order to achieve the above-mentioned object, a groove machining method according to the present invention has a ball holding hole,
Vickers hardness of 1 around the tool holding hole by electric discharge machining
A tool shaft on which about 200 work hardened layers are formed, and the tool
It is held by being pressed into the ball holding hole of the shaft.
A tool consisting of at least one ball,
A grooving method for grooving the surface of a ball by pressing a ball against a workpiece by rotating a tool shaft , wherein the ball has a Vickers hardness of 1200 or more and a modulus of longitudinal elasticity of 250 G
It is a hard spherical body made of silicon nitride of Pa or more.

[0007] manufacturing process of the dynamic pressure bearing of the present invention, the ball holding
It has a hole, and around the ball holding hole by electric discharge machining
A work hardened layer with a Vickers hardness of about 1200 was formed.
Pressing a tool shaft into the ball holding hole of the tool shaft
At least one ball held by
A step of rotating the tool shaft with a tool to press the ball against at least one of a bearing shaft and a bearing sleeve of a dynamic pressure bearing to form a dynamic pressure generating groove on a surface of the ball; Hardness 1200 or more,
It is characterized by being a hard sphere made of silicon nitride having a longitudinal elastic modulus of 250 GPa or more.

[0008]

The ball is mounted on the ball holding hole of the tool shaft. Ball holding hole of the tool axis is for the electrical discharge machining Thus formed, around the ball holding holes are machined hardened material more hard tissues of the tool axis. When mounting the ball in the ball holding hole of the tool shaft, troubles such as damage to the surface of the ball due to friction with the work-hardened portion as described above, loss of sphericity of the ball, etc. occur, Therefore, the precision of the groove processing may be significantly impaired.

Therefore, the ball has a Vickers hardness of 1200.
As described above, by using a hard spherical body made of silicon nitride having a longitudinal elastic modulus of 250 GPa or more, it is possible to prevent the surface of the ball from being damaged or the sphericity of the ball from being impaired to cause deterioration in shape. I do. By using a ball free from troubles such as scratches and shape deterioration, a dynamic pressure generating groove with high shape accuracy can be grooved, and an extremely high performance dynamic pressure bearing can be manufactured.

[0010]

An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a grooving device which is a tool used in a grooving method and a method of manufacturing a dynamic pressure bearing according to an embodiment, which comprises a work holder 2 supported on a processing table 1 and a tip. A holder 4 for rotatably supporting a tool shaft 3 for holding a plurality of balls 31, a rotary drive mechanism 5 for rotating the tool shaft 3, a Z slider 6 reciprocally movable in the vertical direction together with the holder 4, The rotary drive mechanism 5 includes a rotary drive motor 5a, a coupling 5b for transmitting the drive to the tool shaft 3, and a rotary shaft 5c. Comprises a Z drive motor 7a, a coupling 7b for transmitting the drive to the Z slider 6, and a rotating shaft 7c.

The rotary drive mechanism 5 and the Z drive mechanism 7 are driven almost simultaneously, and rotate while vertically lowering the tool shaft 3 with respect to the bearing sleeve W, which is a workpiece held by the work holder 2. As shown in FIG. 2, the ball 31 is pressed against the inner surface of the bearing sleeve W to transfer the shape of the ball 31 to form a dynamic pressure generating groove Wa such as a herringbone groove.

As shown in FIG. 3, the tool shaft 3 has a small-diameter shaft portion 3b having a ball holding hole 3a formed by electric discharge machining, and a large-diameter shaft portion 3c integrated therewith. The portion 3c is integral with the rotating shaft 5c of FIG. 1, and is rotatably supported by the holder 4.

Each of the balls 31 is fixed to the ball holding hole 3a of the tool shaft 3 by press fitting. Each ball 31
Longitudinal elastic modulus of 250 GPa or more and Vickers hardness of 120
0 or more a spherical body of hard, the material is either nitriding silicon
Consisting of

Since the ball holding hole 3a of the tool shaft 3 is formed by electric discharge machining as described above, a work hardened layer such as a molten layer, a quenched layer, and a tempered layer by electric discharge machining is formed around the hole. It is usually formed and hardened to a Vickers hardness of about 900, 1200, or 600, respectively. Therefore, if the ball 31 is softer than the work hardened layer around the ball holding hole 3a when the ball 31 is pressed into the ball holding hole 3a, the surface of the ball 31 is scratched. If it is fixed to the tool shaft 3 with the surface exposed, there is a possibility that a flaw may be transferred to the surface of the bearing sleeve W or the inner surface of the bearing sleeve W may be scraped as described above. The ball 31
If the longitudinal elastic modulus of the ball 31 is equal to or lower than the longitudinal elastic modulus of the tool shaft 3, the ball 31 is plastically deformed when pressed into the ball holding hole 3a, and its sphericity is reduced. There is also a risk.

In this embodiment, the ball 31 is made of silicon nitride having a longitudinal modulus of elasticity of 320 GPa and a Vickers hardness of 1500 as a material of the ball 31, so that the ball 31 is not damaged when the ball 31 is pressed into the ball holding hole 3a. To prevent its sphericity from being reduced.

In recent years, silicon nitride balls have been available inexpensively as bearing balls for heat-resistant bearings.
The amount of sliding wear, which is important as a tool for performing plastic working, is about 1/20 of that of ordinary carbon steel, and it is a suitable material for obtaining a groove machining device with a long tool life. The modulus of elasticity is also generally much higher than the material used for the grooving ball. Therefore, it is the most effective material as a groove machining ball used in the method of manufacturing a dynamic pressure bearing of the present invention.

According to this embodiment, the ball forming the dynamic pressure generating groove such as the herringbone groove on the inner surface of the bearing sleeve is hard, has no scratches on its surface, and has sufficient sphericity. It is possible to manufacture a dynamic pressure bearing having a dynamic pressure generating groove with extremely high shape accuracy. Further, since the tool life of the ball is long, it can greatly contribute to the reduction of the manufacturing cost of the dynamic pressure bearing.

[0019]

Since the present invention is configured as described above, the following effects can be obtained.

By using a ball having no troubles such as scratches and shape deterioration, a dynamic pressure generating groove with high shape accuracy can be machined, and an extremely high performance dynamic pressure bearing can be manufactured. In addition, there is an advantage that the maintenance cost of the apparatus is low because the hardness of the ball is high and the tool life is long, and as a result, the manufacturing cost of the dynamic pressure bearing can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a groove processing apparatus used in a groove processing method and a method of manufacturing a dynamic pressure bearing according to an embodiment.

FIG. 2 is a view for explaining a groove processing step by the apparatus of FIG. 1;

FIG. 3 shows a tool axis and a ball of the apparatus of FIG. 1;
(A) is an elevation view thereof, and (b) is a partial cross-sectional view showing a part of a ball and a tool shaft.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Processing table 2 Work holder 3 Tool axis 3a Ball holding hole 31 Ball

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B21C 37/00-43/04 B21D 53/10 F16C 17/10

Claims (2)

(57) [Claims] 1. A ball holding hole, comprising:
Around 1200 Vickers hardness by electric discharge machining
A tool shaft on which a work hardened layer is formed, and
At least retained by press fitting
Using a tool consisting of one ball, rotate the tool axis
The ball by a groove processing method of grooving the surface against the workpiece, said balls, Vickers hardness 1200 or more, a rigid spherical body consisting of longitudinal elastic coefficient 250GPa or silicon nitride A groove processing method. And a ball holding hole.
Around 1200 Vickers hardness by electric discharge machining
A tool shaft on which a work hardened layer is formed, and
At least retained by press fitting
Using a tool consisting of one ball, rotate the tool axis
And pressing the ball against at least one of a bearing shaft and a bearing sleeve of a dynamic pressure bearing to form a dynamic pressure generating groove on the surface thereof, wherein the ball has a Vickers hardness of 1200 or more and a longitudinal modulus of 250 GPa or more. A method of manufacturing a dynamic pressure bearing, wherein the method is a hard spherical body made of silicon nitride.